I don't know how often it updates but I would guess it's pretty fast.
I have had problems with it myself from time to time though - sometimes it's linked to a price that's completely wrong. The most recent being a Barnsley v Reading fixture.
The teams both played each other twice in the same week and the match it came up with was to the wrong fixture and I backed it by mistake. Always check things as it's only a guide and starting point.
Make it a rule to check everything matches i.e date,team at home,kick off time etc. before placing the bet.....if in doubt.....don't place it.
Sometimes I think I know everything......then I wake up.